I've posted this a few times for others, so it should work for you.
Walk for 2 minutes 50 seconds, jog for 10 seconds. This classes as a cycle. Do 10 cycles per session, so you do a full 30 minutes. Do this 30 minute session 5 days a week, making sure you keep the off days split, so you're not doing 5 days straight.
Second week, change the "cycles" to walking 2 minutes 40 seconds, jog for 20 seconds.
Third week, change the "cycles" to walking 2 minutes 30 seconds, jog for 30 seconds.
You should see a pattern emerging.
When you can get to 30 minutes jogging continuously, then you can make things more interesting, like going for 35 minutes, or using a tougher route, or trying to increase your overall pace.